The Date/Time control panel is not a calendar

The Date/Time control panel is not a calendar

Although many people use the
Date/Time control panel to flip through a calendar,
that's not what it is for.
In fact, if you use it that way, you can create all sorts of havoc!

In its original incarnation in Windows 95, the Date/Time control
panel changed your date and time. If you clicked through the calendar
to see next month, you actually changed your system clock to
next month. If you changed your mind and clicked "Cancel",
the Date/Time control panel undid its changes and restored the date
to the original date.

In other words, here's what happened, step by step:

On April 1, you open the Date/Time control panel.

You change the month to May. The Date/Time control panel
changes your system date to May 1.
If you are running an appointment calendar program,
all appointments from the month of April will fire.
(For example, your April 15th alarm to remind you to file your
income taxes.)
You are annoyed by all these alerts and you cancel them.

You decide you didn't want to change the month to May after all
and click Cancel.

The Date/Time control panel changes the date back to April 1.

On April 15th, your income tax alarm fails to fire
because you cancelled it, remember?

In other words, the Date/Time control panel was not designed for
letting you flip through a calendar. It was designed for
changing the system date and time.

Unaware of its design, people have been using the Date/Time control
panel as if it were a calendar, not realizing that it was doing all sorts
of scary things behind the scenes.
It's like using a cash register as an adding machine. Sure, it
does a great job of adding numbers together, but you're also messing
up the accounting back at the main office!

For Windows 2000, in reluctant recognition of the way people had been
mis-using the Date/Time control panel, it was rewritten so that it
doesn't change the system time until you hit the Apply button.